Craniofacial changes after 80,000 years ago may reflect increased social tolerance

An ambitious study published in the journal Current Anthropology has proposed a link between craniofacial changes and technological advances occurring after around 80,000 years ago. The authors suggest that a reduction in browridge projection and a shortening of the upper facial skeleton (referred to by the authors as ‘feminization’) was the result of either reduced testosterone levels or reduced androgen receptor densities. This reduced male aggression and increased social tolerance, in turn enabling larger groups to live together and the building of long-distance social networks. The consequence was that between around 80,000 and 30,000 years ago, there was acceleration of cumulative technological evolution or ‘cultural ratcheting’ where innovations accumulate over time as a result of cooperation between individuals and groups.

Robert Cieri and his colleagues considered over 1,400 skulls from prehistoric people living before and after 80,000 years ago, and from recent foragers and farmers. They found that a trend towards browridge reduction and facial shortening is apparent from after 80,000 years ago, consistent with the hypothesised higher testosterone levels or androgen receptor densities prior to that time.

The study is the latest attempt to resolve an apparent lag in the archaeological record between the appearance of anatomically modern humans and clear evidence for modern human behaviour in the form of symbolic expression, innovation and planning depth. Such evidence does not become apparent until after 80,000 years ago, leading some anthropologists to postulate a ‘smartness mutation’ occurring at about that time that somehow ‘rewired’ the human brain and enabled it function far more efficiently.

In the last fifteen years or so, the trend has been to look for demographic rather than cognitive explanations. The African Middle Stone Age has examples of seemingly precocious technological traditions such as Stillbay and Howieson’s Poort that were relatively short-lived and were replaced by more conservative traditions. It is argued that periodically, population levels fell to below the level needed to preserve the complex technological traditions from one generation to the next. It has also been suggested that evidence for symbolic behaviour in the form of beads and ornaments is indicative of more complex societies rather than more complex brains. Both fit well with the idea of more tolerant societies emerging after 80,000 years ago.

However, the most recent archaeological data has failed to correlate the disappearance of advanced technological traditions with demographic collapse, and indeed the extent to which such technologies were repeatedly lost has been questioned. For example, microliths are now known to have first appeared 165,000 years ago and their periodic disappearance from the archaeological record may be apparent rather than actual.